1. Field of the Invention
This invention relates generally to implantable devices for vascular interventional therapeutic treatment or vascular surgery, and more particularly concerns a coil with a twisted pattern that exhibits improved flexibility and/or secondary coil shape capabilities along the length of the coil, said coil being particularly useful as a primary coil for more complex shapes used in various vascular interventional therapies.
2. Description of the Related Art
Vasoocclusive devices can take a variety of configurations, and are generally formed of one or more elements that are larger in the deployed configuration than when they are within a delivery catheter prior to placement. One widely used vasoocclusive device is a helical wire coil having a secondary deployed configuration which may be dimensioned to obstruct all or a portion of a particular part of the vasculature of interest. One anatomically shaped vasoocclusive device is known that forms itself into a shape of an anatomical cavity such as an aneurysm and is made of a pre-formed primary coil of flexible material such as a platinum alloy.
The vasoocclusive members can be sized and shaped so that in their deployed configuration they fit within a vascular cavity or vesicle such as for treatment of an aneurysm or fistula. The vasoocclusive member can be first helically wound in a generally linear fashion and is then wound around a mandrel or form shaped to conform with the secondary shape desired, and heat treated to retain the basic shape of the mandrel after removal from the heated form.
A variable stiffness coil that will deform more readily along certain predetermined sections of the coil can be useful for filling aneurysms of various sizes and shapes. A variable cross section conical vasoocclusive coil is known that can achieve variations in stiffness of the coil by variation of the diameter in different regions of the coil or variations in the composition of the coil.
A known method of forming a primary wind coil is to wind a continuous coil of a metal wire such as a platinum wire, for example, on a cylindrical wire mandrel, typically about 0.010 inch in diameter. The resulting primary wind coil typically has the same bending stiffness in all directions because it is formed as a helix about a constant diameter cylindrical mandrel, so that the coil has a constant bending moment about the longitudinal axis of the coil in all planes along the longitudinal axis of the coil.
It would be desirable to provide a flexible metal wire coil for use as a structural element to form a densely packed therapeutic vasoocclusive coil, or clot remover, for example, that allows for the coil to be flexible prior to deployment and to more completely fill and occupy a given space, while retaining the softness of a smaller coil and that can make the delivery of the coil easier. It would also be desirable to provide a primary wind coil that does not have a specific relaxed shape so that it can more completely fill an area to be treated than primary wind coils which are currently available. The present invention meets these and other needs.